Ugh! I just posted and it disappeared! I'll try again!
M and Ns Mom - Could it be overtiredness? Maybe try offering the nap at 12:30. If that doesn't work, slowly move it back in 5 min increments (12:35, 12:40) until you find the sweet spot? When Ds was taking the 30 min AM nap, he wouldn't go down until 3.5 hours afterwards, so it could also be that he isn't tired enough so if an earlier time continues to backfire you could also try moving it later in 15 min increments. I would try to move it earlier first, though, in case it is overtiredness.
kathrynk - I had to laugh at the poop only because the first few days of one nap, DS woke himself up after less than an hour with the same issue. We call them "nap bombs" because when one comes during nap time, it completely destroys any chance of a nap. Give it a few days before you change things up - I found it was a good week or so before the nap stretched out and the bombs stopped, lol. During the first part of the transition, there were a few days where he still needed a short AM nap so we just did it if we had to. Like Stacy, refusing one of the two naps started to become a problem for week or so stretches off and on around 11 months but we didn't successfully make the switch until 14 months (about 4 weeks ago). We found a walk or car ride in the afternoon gave a bit of a rest time when he would refuse the PM nap. Even now that he is on one nap, we give a rest time about 3 hours into his morning A time where we either sit and read stories or watch a Baby Einstein video for 20 min or so with a snack just to give him some time to slow down and recharge. We usually do an outing or walk in the hour or so before dinner to help him get through the second A time stretch before bedtime.
Susan - I think you will likely have to try to push back the AM nap slowly and just at least offer the chance for a snooze in the afternoon. Maybe let the AM go as long as it can go and then put her down for a catnap and give an half hour to try to go to sleep as long as she isn't screaming. If she doesn't go down, go for a walk or a little outing to at least give her some downtime. This will hopefully help her until the transition is done but it will probably be rocky for a while.
Susan -